1. Field of the Invention
The present invention relates to an apparatus and a method for determining whether or not a treatment target substrate is being retained by a substrate-retaining mechanism, and a storage medium for executing the method by a computer.
2. Description of the Prior Art
It has been known in the art a Liquid treatment apparatuses including a substrate-retaining mechanism for retaining a treatment target substrate, particularly a semiconductor wafer (hereinafter, referred to as a wafer), a treatment liquid supply mechanism for supplying a treatment liquid to the treatment target substrate retained by the substrate-retaining mechanism, and a rotation mechanism for rotating the substrate-retaining mechanism that retains the wafer. Such conventional liquid treatment apparatuses have a light-emitting unit positioned above the substrate-retaining mechanism to emit light, and a light-receiving unit positioned below the substrate-retaining mechanism to receive light from the light-emitting unit. As a result, the apparatuses can determine whether or not a wafer is being retained by the substrate-retaining mechanism.
Particularly, it is determined that no wafer is being retained by the substrate-retaining mechanism if light from the light-emitting unit is detected by the light-receiving unit. It is determined that a wafer is being retained by the substrate-retaining mechanism if no light from the light-emitting unit is detected by the light-receiving unit.
Although, the conventional liquid treatment apparatuses can determine whether or not a wafer exists on the substrate-retaining mechanism, they cannot determine whether or not the wafer is being properly retained by the substrate-retaining mechanism.
In addition, it may be erroneously determined that a wafer exists on the substrate-retaining mechanism when a chemical liquid or moisture adheres to the light-receiving unit and prevents it from receiving light from the light-emitting unit. In order to avoid such an erroneous determination, the light-receiving unit needs to be made of an expensive material (e.g. sapphire) that does not react with chemical liquids. This increases the cost for manufacturing the liquid treatment apparatuses.
Furthermore, even if the wafer has been fractured while being rotated by the rotation mechanism, the fracture cannot be instantly detected, and fragments of the wafer may damage components (particularly, valves) of the liquid treatment apparatuses, making it inevitable to repair or replace the damaged components.